No probs man, we've all been stumped by strange car problems at some point lol. If you're considering cams, then go for broke and do them too. I've driven on non-VCT poncams and they were alright... probs have to do it myself if I find the SR20DE cams don't cut it for me with my compression ratio.
If you haven't already, do some research with regard to cams/springs and VCT, since you don't want to delete VCT (you'll lose some response), and the wrong cams/springs can pose a problem. The best people to ask for advice on these forums will be Johnny (Does Pipe Stutututtutu on here and SAU) or Stao (Hypergear on NS and Performance Forums) of Hypergear Turbos. Stao has a thread for Hypergear detailing his testing and the results people got with their combinations. Lots of good info to be had:
http://www.nissansilvia.com/forums/topic/538388-hypergear-sr20det-turbocharger-innovation-evaluation-and-testing/
To be honest, I don't understand why anyone would blame the .86 housing... makes no sense considering power is a peak figure, and bigger housings are aimed to make more power at the sacrifice of response. If anything, a bigger exhaust housing should promote stability by helping to evacuate gas more efficiently, so you should experience fewer problems at the top-end than with a smaller housing.
More confusing is that they would point to housing size as being the cause (i.e. boost comes on too late to make power, so it's just starting to hit peak efficieny at your rev limit), yet power on your dyno graph clearly stops ramping up at 4700rpm when the wastegate is opened by the EBC, power dips sharply at a point where boost is still climbing, then power barely ramps up across 2000rpm at the top-end! Even running N/A it should make a little more power after 5000rpm.
Obviously the .86 housing is not ideal for your SR20, as you get virtually no boost before 4750rpm, however response is an entirely different topic to detonation (i.e. the real reason for the imposed boost limit and that bizarre plateau) and boost ramps up quite smoothly. My understanding is that when turbos limit power it's due to a small turbine housing choking up flow at high rpm, or a small compressor housing failing to generate any more boost in the top end.

"JECs side feeds, flow tested"
Did you get them flow tested, or were they the cheap "high flowed JECS flow-tested remanufactured" injectors off eBay? Those $250 eBay JECs injectors are notoriously bad, either due to inconsistent flow or poor atomisation, so get them tested yourself or replace them with oem-quality injectors like Nismo 750s, a top-mount rail with Bosche injectors (Taarks sell conversion kits for top mount injectors), etc. If you have access to a spare rail with something better than what you have, it could be worth testing. I'd also suggest you check your pump and FPR with a fuel pressure gauge, to confirm that you don't have an issue there. There's a reason the eBay injectors are less than half the cost of reputable gear.
"splitfire coils (blue ones)"
Try some OEM coils if you have access to any. I'm not that trusting of Splitfires, heard too many bad reports in the past, but they might be absolutely fine like your tuner said.
"BKE7 something spark plugs"
Those are one grade colder than OEM which is correct for your power goals. It could be that the spark is blowing out, in which case gap them down to 0.7 or whatever. Search and you'll find threads on that situation.
"In short all at the same time. The intercooler though was what was on the car originally."
Check your intercooler pipes to ensure there aren't any rags lodged in them from the turbo installation. It's happened before.
"The timing was not advanced further due to detonation"
Get hold of a graph of AFRs vs RPM at peak power. If the car is detonating, is it leaning out or running rich? We need more information to diagnose the problem that that dyno sheet.
My money is on the yum-cha JECs injectors, looking at how it ramps up on the graph, holds constant boost, then power goes down, up and all over the place. Do some reading on modified JECs and you might think the same. For example:
http://www.nissansilvia.com/forums/topic/2441472-five-o-motorsport-1000cc-1200cc-side-feed-injectors-review/
https://www.sau.com.au/forums/topic/440013-jecs-injectors-from-usa/
https://www.sau.com.au/forums/topic/364031-jecs-injectors/?page=2

You're over-thinking this. First test the system in an 'uncontrolled' state, see what it does, then decide on your controller.
Disconnect your boost controller and cap all the lines, then disconnect the line going to the wastegate and plug it all up. Get some wire or a ziptie and strap the wastegate lever arm shut, so you're boosting with NO wastegate. Go for a some hot laps up and down your street keeping a close eye on your boost gauge, you don't want to over-boost after all, and see how it performs.
If you aren't hitting 13 psi in that configuration or the pressure builds slowly, then no EBC or reed valve will solve the problem. The best scenario an EBC can achieve is to have the wastegate flap shut 100% until you hit the target pressure, for maximum response, and you're replicating that action for free.
If the boost is weak/lazy with the wastegate out of the picture, the issue is likely going to be related to an intake leak, in which case do a pressure test. The alternative is that the root cause lies in the tune and any components relating to ignition, in which case hook up a Consult cable and Nissan DataScan1, then check out the sensor output for inspiration.

I have a couple of red-top heads spare, whether they have all been dismantled I don't recall, but I can check it out and let you know. Shipping to SA would be a bitch though.
If at all possible, you want a head with matching cam caps. Everything else you can adjust quite easily, whether it be rockers, shims or valve guides, as it's just a question of measuring with a dial gauge and swapping in replacement shims from your parts box or TAARKS. Truth be told, you shouldn't rely on old shims being to spec, given the engine is 20 years old, and reusing shims by replacing them in their original location should be reserved for a quick-and-dirty engine rebuild. I only changed the valve guides and valve stem seals on my head due to time constraints, but at some point I'm sure I'll sort them out and hopefully smooth the valve train out.
The cam caps however need to match the head, or you might have to have a line hone done, and how viable that is depends on wear.

It's quite the ghost town sadly. Many people moved to social media like Facebook, chasing Likes and hoping to extend their e-penis.
SAU still operates, as does JDMST and Performance Forums, however for parts your best bet is probably to join some of the Facebook groups. Just keep in mind that those Facebook groups are teeming with dirtbags, so whilst you can find some bargains, expect to deal with a lot of scum in the process. Good luck man.

Yeah, I had this issue once in the past. The cause was that either the fuse holder wasn't making proper contact with the legs of the blade fuse, or the crimp on the wires leading into the oem fuse box had failed somehow. I tried bulking up the blade fuse legs and twisting them to force contact, and whilst this worked for some time, eventually it was no good. My final solution was to wire in a new inline blade fuse holder (basically a pair of crimped spade sockets and zipties to hold it together, since the shops were closed), and it was a massive pain in the arse to do. There is no cable length in that area, you're on the floor and access is non-existant. If I had to do it again, I'd probably read the FSM and try to pull the fuse holder, and likely the dash in the process.
Simple solution to the problem, but Nissan made it the headache to end all wiring headaches. I could appreciate why people custom wire their track cars after that one.
I will also give you a heads-up on another possible cause, having had this with my horn once before too, and that's internal wire breakage. Whilst the oem wires are quite good quality, they can still be subject to internal oxidation and subesquently the copper can snap despite the insulation looking ok. If you find that rewiring the fuse holder doesn't fix the problem, it's quite likely that the wire snapped further down the line despite appearances. In such a scenario the only solution it to bypass the oem wire and run a new line from one end to another.
In the case of the problem I had with my horn, after I had bypassed the oem wire I removed and and tested the thing, and the insulation immediately separated with minimal force. After all, that was the only part of the wire that was still connected lol.

I have a full set of used China adjustable arms I've been meaning to sell. What level of quality are you looking for David?
These arms worked fine when I ran them several years ago (replaced them for Hardrace gear due to the road noise you get from pillowballs on the street), but they're not expensive. Probs sell the whole lot for $200+post to just clear space.

Depending on the work you're doing, I might have most of the gaskets you need, which I can sell for a decent price (I don't envisage rebuilding another SR20 any time soon). I ended buying 2 OEM VRS S13/redtop gasket kits to rebuild a pair of engines, then plans changed due to one engine being farked, so I took some pieces (mostly valve stem seals iirc) from one of the kits and put the rest on a shelf. This would probably be your best bet at an economical solution.
Let me know what you're doing, and I'll try to remember to check what parts of the kit I have on the weekend.

Easy one to answer:
1. Yes, FRSport is a legit site and I have bought from them before.
2. FRSport is a North American site, not an Australian site. Look at their phone number mate.
3. Googling your exact phrase "SR20 gasket kit" returns Taarks (a.k.a EFI Solutions) and JustJap as the top results, so I have no idea wtf you tried lol:
https://www.efisolutions.com.au/engine-gasket-kit-s13-180sx-sr20det-redtop
http://justjap.com/genuine-nissan-engine-vrs-gasket-kit-nissan-s13.html
4. Taarks and JustJap are legit and I have bought from them.
5. The SR20DET VRS gasket kit is effectively the same as the DE kit, it just has more gaskets. Pretty sure it comes with an o-ring suitable for the DE's distributer. Just make sure you get an S13 kit if your DE engine is from an S13, and an S14 kit if your DE engine is from an S14 or S15 Autech. Look at the rocker cover; flat is S13 and a bump at the front is S14/S15. They use different oil pumps, and that's where the bump comes from, so don't buy the wrong one.

Also remove all the spark plugs when doing the test and hold the throttle open full; comp tests need to be done with no restrictions. Also, be sure to remove the fuel pump fuse (obvious).
Here's something for you to measure against:
Youtube ftw.

Pretty sure you'll be fine, and if I'm wrong about some bizarre CA18 quirk it would be easily rectified, so no need to stress about it. I recall the CA18 uprights being the same as SR20 uprights, and a quick Google search suggests that the SR20 brakes are a straight bolt-on for the CA18, as you would expect them to be.
I run rear S13 uprights and S15 front uprights. I don't remember drilling out any holes in my R33 calipers, and I don't use any form of adapter plates. The caliper bolt holes on the S15 uprights should be identical to the S13 uprights, as a common budget swap used to be S14 calipers with S14 rotor blanks drilled to 4-stud.
All said, I'd be surprised if everything wasn't a straight bolt-on for you if used R33 rotors drilled to 4-stud, or S14/S15 front uprights and S14/15/R33/Z32 rear hubs. The only exception to this is of course that the S14/S15 front uprights that require a 14mm>12mm sleave (https://www.efisolutions.com.au/knuckle-to-strut-adapters-s13-s14-s15), the S13 front LCAs need an S14 balljoint (iirc) to fit the S14/S15 uprights and I recall there being some banjo bolts for the brakes that must be cut to length.